Trenching of Pipelines for Protection in Ice Environments

Subsea pipelines located in ice environments need to be protected from potential ice gouging (also known as ice scouring) created when a moving ice keel interacts with the seabed. The integrity and operability of the pipeline can be affected by direct contact between the ice keel and the pipeline, or from loading imposed on the pipeline through soil deformation caused by ice gouging. The typical method considered for protecting against the risk of damage caused by ice gouging is through pipeline burial. Conventional methods of pipeline burial use equipment such as ploughs, mechanical trenchers, and jetters, the majority of which have been designed to accomplish a maximum of 2-3m of pipeline burial. Dredges can be used, but they have water depth limitations and limited productivity. Land-based equipment has been used for shore crossings, but is limited to shallow water depths where temporary construction berms can be used as a working platform. The capabilities of existing technologies are based on current industry practice developed for pipeline burial in ice free environments. Pipeline burial requirements have generally been for improved hydrodynamic stability, mechanical protection (e.g. from anchors), controlling pipeline movements (e.g. expansion and buckling) and/or for flow assurance purposes (reducing heat loss). A 2-3m burial depth has been generally adequate to satisfy these conventional requirements. As developments are proposed for areas that experience relatively deep ice gouging (up to 5m), burial depth requirements will exceed the capabilities of current pipeline burial technologies. New technologies capable of working in deeper water, achieving greater burial depths, achieving reasonable trenching advance rates, operating in harsh environments, and trenching through variable and difficult seabed soils will be required. This paper highlights the issues and challenges surrounding pipeline trenching and burial in ice gouge environments. Current state-of-practice is discussed along with the technology gaps that need to be addressed to prepare for future offshore developments in ice-covered waters where there is the potential for seabed ice gouging.